Pulsed lasers such as a copper vapor laser, an excimer laser, and a carbon dioxide laser require a discharge tube for providing energy for excitation and a pulsed power supply device for causing the discharge tube to emit light.
To provide large laser output power, the pulsed power supply device needs to produce very large power and large power consumption occurs there. Therefore, it is desired that the pulsed power supply device be improved in operation efficiency.
FIG. 10 shows a conventional pulsed power supply device disclosed in Japanese Unexamined Patent Publication No. Hei. 4-349677, for example. In the figure, reference numeral 1 denotes an AC power source that supplies power; 2, a DC voltage source that has the AC power source 1 as an input and generates a high DC voltage; 3, a capacitor that is connected in parallel to the output of the DC voltage source 2 and stores a high voltage; 4, a switch that is connected to the capacitor 3 and releases the energy stored in the capacitor 3 through a discharge; 5, a reactor provided in series with the switch 4 in the discharge route of the capacitor 3; and 6, a capacitor provided between the output side of the reactor 5 and one pole of the DC voltage source 2.
Reference numerals 7 and 8 denote a saturable reactor and a peaking capacitor, respectively, provided in the discharge route of the capacitor 6. Reference numeral 9 denotes a discharge tube connected in parallel to the peaking capacitor 8. Reference numeral 11 denotes a diode for rectifying a reverse-polarity voltage across the capacitor 6 and inputting a rectified voltage to a transformer 10, numeral 12 denotes a high-frequency bypass capacitor provided on the output side of the transformer 10, and numeral 13 denotes an inverter that has the voltage across the capacitor 12 as an input and whose output serves as an input of the DC voltage source 2, that is, whose output is connected in parallel to the AC power source 1.
Next, the operation of the pulsed power supply device of FIG. 10 will be described with reference to a time chart of FIG. 11.
First, the capacitor 3 is charged to have a high voltage by the DC voltage source 2 that is powered by the AC power source 1. Then, as soon as the switched 4 is turned on at time t1, the charge of the capacitor 3 is released via the reactor 5 and the capacitor 6 is charged quickly. During this charging process, the saturable reactor 7 prevents charging of the peaking capacitor 8. When in due course the saturable reactor 7 has been saturated at time t2 and the circuit inductance has decreased greatly, discharging of the capacitor 6 and charging from the capacitor 6 to the peaking capacitor 8 is started. When the voltage across the peaking capacitor 8 has reached a predetermined value at time t3, the discharge tube 9 is discharged and comes to exhibit low impedance, whereby the peaking capacitor 8 is discharged. The switch 4 is opened when the voltage across the capacitor 3 has become approximately zero. Pulses are generated repetitively by repeating the above operation.
In the above operation, a current is supplied to each of the capacitor 6, the peaking capacitor 8, and the discharge tube 9 by a resonance phenomenon caused by the capacitance of the capacitors involved and the circuit inductance. The resonance frequency gradually increases (that is, the pulse duration gradually decreases and the peak voltage increases) by making a setting that a capacitor closer to the last stage has a smaller capacitance value. Finally, a large, steep current flows through the discharge tube 9.
The above type of circuit is called a magnetic compression circuit or a pulse compression circuit (the term "pulse compression circuit" will be used hereinafter). In this pulse compression circuit, an oscillation phenomenon is utilized in the above manner in transferring energy from an upstream capacitor to a downstream capacitor. If the circuit constants were not appropriate and the circuits were not matched with each other in discharge impedance, voltages would remain in the capacitor 6 and the peaking capacitor 8 after a discharge. There is an outstanding subject that such residual energy should be minimized. For example, Japanese Unexamined Patent Publication No. Hei. 4-200281 discloses that the capacitance ratio of upstream and downstream capacitors is set at 1:0.7 to 1:1.
In the device of FIG. 10, a voltage having a reverse polarity generated across the capacitor 6 by an oscillation (resonance) phenomenon is applied between the input terminals of the transformer 10 with the diode 11 turned on. Therefore, a current flows through the diode 11 and the transformer 10 from the capacitor 6 or the peaking capacitor 8, to charge the capacitor 12 that is connected to the output side of the transformer 10. And the energy that has not been dissipated by the resistance component of the circuit during the resonance phenomenon is stored in the capacitor 12. The energy stored in the capacitor 12 is converted to an AC voltage by the inverter 13 and reused as an input of the DC voltage source 2.
The above-described method in which energy is recollected via an AC circuit has a problem of large energy loss in the stage of AC-to-DC conversion.
A second background technique is known that is intended to solve this problem. In this technique, as disclosed in Japanese Unexamined Patent Publication No. Hei. 9-148657, for example, a secondary winding is provided in a saturation transformer (corresponding to the saturating reactor 7 shown in FIG. 10) in a DC circuit and energy is recollected so as to be supplied to the DC side of the DC voltage source 2 via an energy regeneration circuit that is connected to the secondary winding.
In the conventional pulsed power supply device having the above configuration, unnecessary power that is not consumed in the discharge tube is regenerated via AC devices such as a transformer and an inverter. Therefore, the conventional pulsed power supply device is voluminous and costly. Further, since regenerated power occurs on the AC input side, the output capacity of the DC voltage source is required to accommodate such excess power and hence the DC voltage source becomes voluminous. Since power is regenerated via many devices such as a DC voltage source, a transformer, and an inverter, there arises a problem that power loss in the circuit makes it difficult to increase the efficiency.
Because regenerated energy occurs on the DC output side of the DC voltage source, the second background technique is free of the above kind of loss in efficiency and economy that is caused by the AC circuit. However, since a current flowing through the saturable reactor is regenerated via the secondary winding, there is a problem that the loss is large and the efficiency is not high.
The present invention has been made to solve the above problems, and an object of the invention is therefore to enable high-efficiency regeneration of power, specifically, a voltage (energy) remaining in a capacitor of a DC circuit only by means of the output side of a DC voltage source without requiring AC devices such as an inverter and a transformer and to make it unnecessary to provide a secondary winding in a reactor, to thereby reduce the output capacity of the DC power source, increase the efficiency of a pulsed power supply device, and decrease its size and cost.
Another object of the invention is to present a more appropriate selection range of circuit constants in further increasing the voltage of generated pulses by using a pulse width compression circuit in a pulsed power supply device that has been invented to attain the above object.